Abatement of Cr(VI) and As(III) by MnO₂ loaded MCM-41 in wastewater treatment

Manganese dioxide (MnO₂) loaded MCM-41 (MnO₂/MCM-41) was used as adsorbent to remove Cr(VI) and As(III) from aqueous solution. The adsorbent was synthesized and characterized. Effect of pH on the removal of Cr(VI) and As(III) was investigated. The desired pH of aqueous solution was 2 for the removal of Cr(VI) and 4 for the removal of As(III). Besides, the adsorption of As(III) and Cr(VI) can be well described by Langmuir and Freundlich isotherm models, respectively. The kinetic data can be successfully depicted by pseudo-second-order model. Moreover, external and intra-particle diffusion were found to be rate-controlling steps of the adsorption process. Thermodynamic analysis suggested that the adsorption process was spontaneous and endothermic. In a binary system, the presence of Cr(VI) and As(III) slightly reduced the removal efficiency of each other. The desorption study showed 0.1mol/L NaOH liquor held good desorption ability for metal loaded MnO₂/MCM-41.